Competitive interaction between the plants of sunflower and weeds in agrocenosis

Purpose. To determine the mutual influence of the weed component and the cultivated plant in the agrophytocenosis of sunflower during joint vegetation. Methods. Field, laboratory, quantitative-weight, calculation-comparative, mathematical-statistical. Results. The results of studies of weed infestation of sunflower crops under different periods of joint vegetation are highlighted. The species composition of weed plants in sunflower crops was represented by 15 species from 10 families, a mixed type of weed infestation with a predominance of dicotyledonous species – 56.3%, monocotyledonous – 43.7%. The most common species were: Chenopodium album L. (42%), Echinochloa crus-galli L. (30%), Setaria glauca L. (13%), Amaranthus retroflexus L. (7%). Sunflower yield depended on the period of joint vegetation of the crop with weeds: the longer is the period of joint vegetation, the greater are the losses. The smallest losses in sunflower yield (7.9% and 12.2%) were under the condition of destruction of weeds after 10 and 20 days. Continuation of joint vegetation of the crop and weeds for 30 or more days leads to a decrease in yield by 17.6-40.1%. Under the condition of joint vegetation of sunflower with weeds during the entire growth period, the losses amounted to 47.7%, or 1.57 t/ha. The yield of sunflower seeds in the control variant without weeds was 3.29 t/ha. Conclusions. The most effective period for controlling weed infestation of sunflower crops is the first 10-20 days, which leads to the smallest yield losses (7.9-12.2%). Reducing the period of joint vegetation of the crop with weeds from 60 to 10 days led to the preservation of yield at the level of 1.97-3.03 t/ha, losses amounted to 40.1 to 7.9% depending on the number of days. Studies have shown that even a small delay in weed control can cause significant loss of sunflower crops yield.